Invasion of native plant communities by exotic perennial grasses was listed as a KEY THREATENING PROCESS on Schedule 3 of the Threatened Species Conservation Act 1995 [12 September 2003].
Exotic perennial grasses are those that are not native to NSW and have a life-span of more than one growing season. More than a hundred species of exotic perennial grasses occur in New South Wales. A relatively small number of these perennial grasses threaten native plant communities, and it is these species which are of concern.
Exotic perennial grasses of special concern include Hyparrhenia hirta (Coolatai grass), Cortaderia spp. (pampas grasses), Sporobolus fertilis (giant Parramatta grass), Nassella neesiana (Chilean needlegrass), Nassella trichotoma (serrated tussock) and Eragrostis curvula (African lovegrass).
The listing of “Invasion of native plant communities by exotic perennial grasses” as a key threatening process has been made in recognition of the increasing evidence that some perennial grass species have significant adverse impacts on biodiversity. A few examples follow:
- Coolatai grass grows vigorously forming an almost complete monoculture replacing native grass and wildflower species. It tolerates drought, heavy grazing and many herbicides. It has invaded large areas of grassy woodlands and native pastures in north-west NSW and is spreading rapidly in other regions.
- Chilean needlegrass has several features which give it a competitive advantage over many native species, such as its ability to produce a large, long-living seed bank, high survival of seedlings, tolerance to drought and effective animal-borne and water-borne dispersal mechanisms for seeds.
- Serrated tussock infests more than a million hectares in southern Australia but has the potential to spread over a much larger area. It invades native grasslands, grassy woodlands, dry forests and rocky shrublands. Serrated tussock forms large tussocks with individual plants capable of producing more than 10,000 seeds annually. Some seeds remain viable in the soil for more than 10 years. Mature plants droop across the ground smothering other species.
- Pampas grass readily tolerates saline conditions, salt spray, drought, periodic inundation, severe frosts, strong winds and can grow on a wide range of soil conditions and light conditions (from shaded areas through to full sunlight). Pampas grass is an aggressive coloniser and can form dense stands which prevent other plants from growing. Individual flower heads produce more than 100,000 seeds and wind may disperse seed for several kilometres.
- Perennial grasses, such as perennial veldtgrass, pampas grass, Coolatai grass and buffel grass, produce large amounts of plant matter which dries quickly and causes fuel loads to increase. This fuel results in fire regimes that favour the spread of these perennial grasses. Hotter and more frequent fires may lead to changes in the structure of the vegetation and in some cases to local extinctions of some plant and animal species.
Several endangered ecological communities are threatened by exotic perennial grasses. Examples include the following:
- White Box Yellow Box Blakelys Red Gum woodland is threatened by Coolatai grass. Coolatai grass dominates large areas of pasture, roadsides, travelling stock routes and areas of remnant vegetation in the North Western Slopes, especially in the Manilla area north of Tamworth.
- Serrated tussock, African lovegrass and Chilean Needlegrass are a major threat to native grasslands, particularly the endangered communities Natural Temperate Grasslands of the Southern Tablelands of NSW and the ACT and Bega Dry Grass Forest.
- In the Sydney area, pampas grass threatens Duffys Forest Ecological Community. Threatened species at risk include Persoonia mollis and the orchid Microtis angusii.
A Saving Our Species conservation project is currently being developed for this species and will be available soon. For information on how you can contribute to this species' recovery, see the Activities to assist this species section below.